This invention relates to electrical apparatus for powering automatic camera equipment in a manner to avoid interference between camera operations. More particularly, the invention provides electrical control apparatus which limits the charging of a photographic flash capacitor to selected operating conditions when other interference-sensitive elements of the camera system are quiescent. The invention is described with particular reference to an electronic flash unit having control means which inhibits the charging operation when a sonic ranging device for automatic camera focusing is active.
Electronic flash units for photography are well known. The units conventionally have a battery-powered oscillator for producing alternating voltage which is rectified to charge a flash-powering storage capacitor. It is also known to control this capacitor-charging operation due to restrictions on the available battery power. The prior art on this subject includes U.S. Pat. Nos. 3,846,812; 4,001,639 and 4,064,519.
The advent of automatic focusing for cameras by sonic ranging raises the problem of a focusing malfunction due to interference with radiation from the flash unit. The focusing system emits sonic energy and positions the objective lens of the camera in response to reflections sensed from the object to be photographed. However, faulty ranging can occur when the focusing system picks up stray radiation from the capacitor-charging oscillator of the flash unit. The result of such faulty ranging operation is improper focusing of the objective lens of the camera and consequently an improperly focused photograph. It is understood that the interfering radiation is electromagnetic in nature.
The use of shielding to contain electromagnetic radiation from the flash-unit oscillator, and the use of selected frequency ranges for the ranging system and for the oscillator can diminish the interference problem, but recourse to these solutions tends to be costly. Moreover, the complete isolation of the ranging system from the capacitor-charging oscillator with either technique, so that the likelihood of a ranging malfunction is rendered negligible, is elusive to attain.
The prior art regarding automatic camera focusing includes U.S. Pat. No. 3,522,764, and commonly-assigned pending applications Ser. Nos. 729,289 for "Automatic Focusing Camera" by E. Shenk and Ser. No. 729,392 for "Ultrasonic Ranging System For Camera" by J. Muggli.
It is an object of this invention to provide apparatus for controlling photographic electronic flash equipment to operate without interference with sonic ranging for automatic camera focusing. To this end it is an object of the invention to provide photographic electronic flash equipment which responds to electrical signals available from an automatic sonic-focusing camera for controlling the capacitor-charging oscillator for operation without electromagnetic interference with the camera focusing operation. It is a further object of the invention to provide flash equipment-controlling apparatus of the above character which requires few components, and is otherwise comparatively low in cost.
A specific object of the invention is to provide a regulated photographic electronic flash unit incorporating control apparatus for operation without interfering with automatic camera focusing.
It is also an object of the invention to provide apparatus of the above character which operates with a minimum of operator attention or concern.
Other objects of the invention will in part be obvious and will in part appear hereinafter.